We plan to study the mechanisms by which glucocorticoids and proteolytic enzymes such as trypsin and thrombin initiate cell division. Our studies on glucocorticoids will be directed at examining the changes in specific growth factor binding that occur after treatment with dexamethasone, a synthetic glucocorticoid. We plan to further study the relationship between the modulation of growth factor binding by dex and the modulation of the action of these growth factors by dex. Our efforts will be directed at the question of whether the modulations of growth factor binding are causally involved in the modulation of growth factor action. Our studies on the mechanisms by which proteolytic enzymes initiate cell division will be based on our findings that for both thrombin and trypsin, action at the cell surface is sufficient to initiate cell proliferation. We now plan to look for cell surface proteolytic cleavages that are causally involved in this initiation. These studies will employ cell surface labeling by the 125I-lactoperoxidase technique followed by one or two-dimensional electrophoresis and autoradiography.